doi:  10.3878/j.issn.1006-9895.1702.16101
出流边界对京津冀地区强对流局地新生及快速增强的动力效应

Dynamical Effect of Outflow Boundary on Localized Initiation and Rapid Enhancement of Severe Convection over Beijing-Tianjin-Hebei Region
摘要点击 608  全文点击 572  投稿时间:2015-12-31  
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基金:  公益性行业(气象)科研专项GYHY201306008、GYHY201506004,国家自然科学基金项目41575050、41075036
中文关键词:  对流风暴  出流边界  雷达  四维变分同化
英文关键词:  Convective storm  Outflow boundary  Radar  4DVar (4D variational assimilation)
        
作者中文名作者英文名单位
陈明轩CHEN Mingxuan中国气象局北京城市气象研究所, 北京 100089;南京大学大气科学学院, 南京 210046
肖现XIAO Xian中国气象局北京城市气象研究所, 北京 100089
高峰GAO Feng中国气象局北京城市气象研究所, 北京 100089
引用:陈明轩,肖现,高峰.2017.出流边界对京津冀地区强对流局地新生及快速增强的动力效应[J].大气科学,41(5):897-917,doi:10.3878/j.issn.1006-9895.1702.16101.
Citation:CHEN Mingxuan,XIAO Xian,GAO Feng.2017.Dynamical Effect of Outflow Boundary on Localized Initiation and Rapid Enhancement of Severe Convection over Beijing-Tianjin-Hebei Region[J].Chinese Journal of Atmospheric Sciences (in Chinese),41(5):897-917,doi:10.3878/j.issn.1006-9895.1702.16101.
中文摘要:
      针对2014年7月16日发生在京津冀地区包含三次风暴过程的强对流"事件",通过雷达、探空和自动站等观测资料分析,以及基于雷达资料快速刷新四维变分同化(RR4DVar)和三维数值云模式的高分辨率模拟,研究了在京津冀复杂地形条件下导致对流风暴局地新生及快速增强的对流尺度热力和动力机制,重点分析了出流边界在对流风暴局地新生及快速增强过程中的动力效应。探空观测和模拟结果均显示,16日当天从上午到傍晚,京津冀地区存在有利于对流风暴发生、发展的中尺度环境条件,包括明显的热力不稳定、强的偏南低空急流和低层垂直风切变等。在本次强对流"事件"中,首先是东移的近地面切变线在中午12:00(北京时,下同)左右触发了天津地区多单体对流风暴的局地新生和快速加强,并产生了明显的向西北移动的出流边界。随后,在京津冀西北部山区形成的一个产生向南出流的风暴单体于下午18:00左右抵达北京西北部山边,由于地形强迫,沿山坡加速下滑的风暴出流与沿山坡上行的低层偏南暖湿气流相互作用,增强了山坡附近的低层辐合和垂直上升,同时在向南和向西北移动的出流边界"碰撞"形成的动力不稳定配合下,使得风暴单体在下山过程中迅速发展为强超级单体风暴。两条出流边界在风暴附近的"碰撞"及其和低层偏南暖湿气流的相互作用,具有复杂地形条件下导致风暴新生和加强的"三重点"关键区特征。在22:00左右,由超级单体风暴形成的出流边界抵达京津冀南部平原地区,与偏南低空急流和低层偏东风湿空气产生的辐合区相互作用,形成新的类似于"三重点"的关键区,导致在辐合区内沿出流边界出现暖湿空气的强烈上升。在出流边界的动力不稳定触发下,沿出流边界附近不断有对流单体新生和增强,最终在23:00左右形成了一条近似东西走向的线状多单体风暴系统。
Abstract:
      This study is focused on a strong convective event that included three convective storms occurred in Beijing-Tianjin-Hebei region on 16 July 2014. Convective-scale dynamical and thermo-dynamical mechanisms are presented to clarify dynamical effects of outflow boundaries on localized initiation and rapid enhancement of convective storms over the complex terrain area in the region mentioned above using observations from radars, radiosondes, and auto weather stations and high-resolution numerical results simulated by a rapid-refresh 4D variational assimilation (RR4DVar) of multi-radar observations and a 3D cloud-scale numerical model. The results from radiosonde observations and high-resolution simulations indicate that meso-scale environmental conditions including a strong thermal instability, a low-level southerly warm and moist flow (jet), and a low-level vertical shear were favorable for the initiation and development of convective storms in the region from the daytime to nighttime on 16 July. The localized initiation and rapid intensification of a multi-cell storm over Tianjin area was first triggered by an eastward-moving near-surface shear line at about 1200 BJT (Beijing time) during the period of the strong convective event. Meanwhile, a northwestward-moving strong outflow boundary was generated by the strong convective storm. At about 1800 BJT, a new storm cell that formed over the northwestern mountains of the region in the early afternoon reached the mountains to the northwest of Beijing with southward outflow. Due to the topographic forcing, strong low-level convergence and updraft occurred over the mountain slope due to the interaction between the storm outflow that accelerated down the slope and the low-level warm and moist southerly flow that moved up along the mountain slope. Meanwhile, dynamical instability developed and superposed on the slope because of the collision of the southward-moving and northwestward-moving outflow boundaries. Under the influence of the factors mentioned above, the storm cell rapidly evolved into a strong supercell storm while it went down the slope. Characteristics of circulation over the key area were similar to that in the so called "triple point" area for storm initiation and intensification in complex terrain area in this region, where two outflow boundaries collided near the storm and interacted with the low-level southerly jet. At about 2200 BJT when the outflow boundary generated by the supercell reached the southern plain, a new key area with properties similar to the "triple point" properties formed due to interaction between the boundary and the convergence area formed by low-level southerly jet and easterly moist flow, which resulted in strong updrafts of warm and moist air along the boundary in the convergence area. As a result of the boundary triggering, convective cells continuously initiated and intensified along the boundary and its adjacent area, and finally formed a multi-cell storm line (squall line) that oriented approximately along west-east direction at about 2300 BJT.
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